Known continuous steel casting methods produce sections two inches (2") (50 mm.) or thicker by width by casting through solid water cooled copper molds in either a vertical or curved configuration. The main problem with such casting is that solid molds intrinsically have a potential for causing defects in cast steel, and thick slabs cast through solid molds to be reduced to sheet or plate must be reheated and rerolled on large, highly complex, energy inefficient equipment with high capital and operating costs.
The prior art is plagued not only by the technical problems and costs associated with slab casting but also by failures in recent world wide initiatives in thin sheet or plate casting. These have consisted of flowing liquid steel by pour and meniscus over mechanical water cooled rolls either single or double roll configuration or alternately casting molten steel between two continuous water cooled moving belts. The major problems with these methods are 1) the poor surface quality resulting from the mechanical impingement of rolls or belts on the liquid steel; 2) the containment of a liquid steel pool between mechanical rolls or belts and 3) shell sticking caused by free meniscus overflow.
A further initiative on near net shape sheet or plate casting is the approach of levitating a thin molten steel section in a super high energy electromagnetic field until it freezes, but this method is ubiquitously recognized as totally cost ineffective.
One known method of float casting liquid steel likewise has known disadvantages. U.S. Pat. No. 4,955,430 to Sherwood discloses float casting molten steel on a molten lead substrate. The question of the immiscibility of lead with iron becomes moot in practice: the vapor pressure of molten lead is so high that at 1600.degree. C. a violent boiling action drives lead into and even through the cast liquid steel as it freezes, entraining large particles of lead (1 to 2 cm.) in and on the surface of the steel. In addition, intense fuming of lead at these temperatures creates an insurmountable environmental problem.
A need remains, therefore, for a float method for casting liquid steel which gives satisfactory sheet casting without the energy inefficiency and inferior quality characteristic of prior art processes.